1. Field of the Invention
The present invention relates to a driving circuit of an AC fan motor and more particularly to an AC fan motor driving circuit providing a current wave detecting capability to adjust the operating status of AC fan motor.
2. Description of Related Art
With reference to FIG. 4, one driving circuit of one AC fan motor has an AC to DC converter (20), a regulated voltage divider (21), a motor driving unit (22), two windings (23), a harmonic wave suppression unit (24) and an current protection unit (25).
The AC to DC converter (20) is connected to the AC power through the current protection unit (25). The AC to DC converter (20) coverts the AC power to high voltage DC power and then outputs the high voltage DC power to regulated voltage divider (21).
With further reference to FIG. 5, the regulated voltage divider (21) has a large resistor, a node and a zener diode (ZD1) connected in series. The large resistor is connected to the AC to DC converter, and may be two large resistors (R1, R2). The node is connected to the large resistor. The zener diode (ZD1) has a breakdown voltage, is connected between the node and ground and operates at the breakdown voltage. Consequently, a regulated low voltage is dropped across the zener diode (ZD1) and provided at the node.
The motor driving unit (22) is connected to the regulated voltage divider (21) to obtain low voltage DC power and has a first transistor (Q1), a second transistor (Q2), a driving IC (IC1) and a Hall sensor (H1). Each transistor (Q1, Q2) has a base terminal (B), a collector terminal (C) and an emitter terminal (E). The driving IC (IC1) has a low voltage DC input, two Hall signal inputs (H+, H−) and two control outputs (O1, O2). The low voltage DC input is connected to the node in the regulated voltage divider (21). The two control outputs (O1, O2) are connected respectively to the base terminals (B) of the transistors (Q1, Q2). The Hall sensor (H1) is connected to the Hall signal inputs (H+, H−) of the driving IC (IC1) and has a low voltage DC input connected to the node in the regulated voltage divider (21). Therefore, the driving IC (IC1) output controlling signals to the base terminals (B) of the transistors (Q1, Q2) to alternately turns the transistors (Q1, Q2) on and off according to the Hall signals from the Hall sensor.
The windings (23) have a first winding (L1) and a second winding (L2) and are connected to the high voltage DC power, the filter (C1) and respectively to the collector terminals (C) of the transistors (Q1, Q2). Since the windings (23) are directly connected to high voltage DC power, a large current is passed through the windings (23). To prevent the windings (23) from being damaged by the large current, each winding (L1, L2) has many coils to increase the resistance. Therefore, the large current will be held in a suitable range to increase the rotation rate of the AC fan motor, and the windings (L1, L2) will not be damaged.
The harmonic wave suppression unit (24) is connected to the high voltage DC power in parallel with the windings (L1, L2) and has two diodes (D2, D3) and a zener diode (ZD2). Each diode (D2, D3, ZD2) has a negative terminal and a positive terminal. The negative terminals of the two diodes (D2, D3) and the zener diode (ZD2) are connected together. The positive terminals of the two diodes (D2, D3) are connected respectively to the collector terminals (C) of the transistors (Q1, Q2). The positive terminal of the zener diode (ZD2) is connected to the high voltage DC power and the filter (C1) to obtain high voltage DC power.
In the driving circuit, the driving IC and Hall sensor are important elements to keep the AC motor in a steady situation. However, the present driving circuit does not have a detecting current through the windings function so the operator can not further adjust the operating status of the AC motor.
Further, the regulated voltage divider uses the two large resistors and zener diode to divide to low voltage, but the two large resistors are easily heated to reduce useful life, since the large current passes through the two large resistors when they are connected to high voltage DC power.
Therefore, the present invention provides a driving circuit of an AC fan motor to add the detecting current wave function and increase the useful life of the regulated voltage divider.